I play Realms Bedrock edition of Minecraft. I think the issue listed below start in version 1.2.5 and has continued since then.

The bug:

Damage is sometimes received when moving out of a nether portal. Moving into the portal in the over world causes no damage but on the nether side damage can be received. If time was spent standing in the portal upon arrival a significant amount of damage is received, up to and including death.

Some portals only cause damage when moving into the nether, while other portals cause damage both ways. Some portals consistently cause more damage than others.

I initially thought the damage was caused because the portal was build against a wall and that materialising in the wall caused suffocation. However, I recently removed walls from both sides of my portals in the nether and the over world but the damage still occurs.